192-element 1.5D phased array with elliptic footprint

More than one third of adults and 17% of youths were obese in 2009-2010 in the US. The scan depth for a person with a waist of 130 cm in circumference is more than 30 cm. More than 3% of ultrasound studies are limited by bad image quality at large depths. The objective of this work was to design a transducer that will produce an image whose quality at a depth of 30 cm is comparable to the quality of an image at 20 cm acquired with a state-of-the-art curved linear array. Image quality can be quantified by penetration depth, detail resolution, and contrast resolution. An existing transducer, 8820e, by BK Medical was used as a baseline for comparison of the new design. 43 dB increase in signal-to-noise ratio (SNR) is needed to increase scan depth from 20 to 30 cm. The transducer-related factors that increase the penetration are: (a) lower frequency; (b) higher number of active channels; (c) larger element size; (d) focusing in elevation. We investigated 22 different designs in simulation: 10 curved, 6 linear, and 6 phased arrays. We varied curvature, pitch, element height and elevation focus. A 1.5D phased array was designed using the experience from the 22 designs. The middle row has 128 elements and the outer rows have 64 elements, giving an elliptical footprint of the probe and allowing for a scanner with 192 channels to use all elements all the time. Point spread functions (PSF) for depths 0 to 30 cm were simulated in Field II in 0.5 cm steps. All of the 22 designs have amplitude at 30 cm larger than the signal level from 8820e at depth of 20cm. Based on PSF we chose two candidate designs: a curved linear array and a 1.5D phased array. We built two prototypes - 88jj is the prototype of the curved array and p3c is the prototype of the 1.5D phased array. The p3c prototype (3 × 192 elements, outer rows connected) allowed us to connect any 192 elements to a 192-channel system. Evaluations on phantoms and in-vivo show that the performance of P3C is comparable t- that of 88jj at depths from 15 to 25 cm, and to 8820e at depths 0 to 15 cm.